Such an extrusion head has become known from DE 34 30 062 C2 and, in another form of realization, from DE 37 36 231 A1. Both forms clamp the movable parts of the extrusion head together not by means of clamps and fast on the fixed extrusion head part, as is the case in DE 22 01 631 C3 and DE 22 36 363 A1 where the holding forces are absorbed by clamps which are displaced by piston-cylinder units and secured in their closing position, but rather they provide the necessary closing forces solely by piston-cylinder units. This makes it necessary to use very sturdy piston-cylinder units. These are very heavy and hard to move.
In the case of DE 34 30 062 C2, the piston-cylinder unit is articulated at its one end pivotable outwardly on the fixed part of the extrusion head; a pin fastened to the unit is displaceable in a sliding block in the form of an obliquely oriented slot. During the opening process, the piston-cylinder unit is pushed outward under the influence of this sliding block link, so that the tie rods are pivoted out of the movement path of the pivotable extrusion head parts for the opening process thereof. The pivoting of the piston-cylinder units moving the tie rods is so complex that a different solution was sought in DE 37 36 321 A1. This was realized with fixed piston-cylinder units whose piston rod is rotated during its displacement movement by means of a sliding block. At its free end, the piston rod carries a hammer head type part which engages behind two projections on the pivotable extrusion head part and by means of them transmits the closing forces to the pivotable extrusion head part. To open the extrusion head, first the tie rod is released, then the hammer head thereof is rotated 90 degrees, and then retracted between the two projections to clear the way for pivoting the associated pivotal extrusion head part. Long piston-cylinder units, a complex rotating mechanism, and long closing and opening times are the disadvantages of this known extrusion head.
In DE 42 36 120 C1 there is disclosed an extrusion head for extrusion apparatus of the rubber or plastic industry consisting of a stationary part flanged on an extrusion installation and at least one movable part which is hinged on the stationary part and, for cleaning purposes, movable by means of a piston-cylinder unit between open and closed positions and is clamped in closed position by a pair of draw bars actuated by a further piston-cylinder unit. The coordination of movement of the several parts of the mechanism presented difficulty in operation of the apparatus.